Protective device for electric circuits



y 8, 1940. A. M. SCHMIDT PROTECTIVE DEVICE FOR ELECTRIC CIRCUITS Filed Feb. 24, 1938 INSULATION l Inventor: Alfred M. Schmidt, by Wan/1 v w/1W His Attorney.

Patented May 28, 19 40 UNITED STATES PATENT OFFICE PROTECTIVE DEVICE FOR ELECTRIC CIRCUITS Application February 24, 1938, Serial No. 192,382 In Germany February 27, 1937 2 Claims.

The present invention relates to protective devices for electric circuits, more particularly fuse devices, and has for one of its objects the provision of an improved fuse device having means 5 whereby control of the operation of the fuse device may be effected from a point remote from the device either by manual switching or in dependency upon an electric condition at such remote point.

Another object of the invention is the provision of an improved construction and arrangement of parts in an enclosed or cartridge fuse of the type embodying one or more fusible conductors embedded in an arc-quenching filler such as a relatively finely divided refractory in- -ulating material, as for example, quartz sand.

Other objects and the details of that which I believe to be novel and my invention will be-= come apparent from the following description 2 and the claims appended thereto taken in conjunction with the aecompanying drawing in which Fig. 1 shows a longitudinal section of an exemplary form of fuse device embodying my invention; Fig. 2 is a plan view of the ,device of Fig. 1; and Fig. 3 illustrates a modification thereof.

Referring to the drawing, i0 designates an open-ended tubular casing of insulating material, the opposite ends of which casing are closed by contact or terminal plates H and I2 respective- ;0 ly. These plates have portions bent over so as to extend respectively along two opposite sides of the casing, and the bent over portions of the plates are formed with contact lugs ii and i2 projecting outwardly from the casing substan- 35 tially in a common plane passing through the longitudinal axis of the casing. The advantage of a contact lug arrangement such as just described, is that it may be employed in the mounting of fuse devices of different lengths between stationary supporting contacts having a certain fixed spacing. A further advantage of the described lug arrangement is that it leaves the ends of the casing free for application thereto of other means, such as the remote control-means ,5 hereinafter described.

Terminal plates ii and 92 are adapted to have connected therebetween one or more fusible conductors, two of such conductors, designated l3, being employed in the embodiment of Fig. l,

0 and one of such conductors being employed in the embodiment of Fig. 3. One end of each of the conductors is secured to terminal plate 02 in any suitable manner, as for example, by soldering. The other ends of the conductors of Fig.

5 1 are secured respectively in openings I4, provided in terminal plate H, by means of small bodies of relatively low melting point solder, as indicated at l5. Conductors l3 are embedded in a body I6 of relatively finely divided, refractory insulating and arc-quenching material, such as 8 quartz sand, which fills casing. Hi.

On the outside of plate ii is secured a casing I! which carries two connection terminals I 8 respectively on opposite sides thereof. These terminals serve to support a heater element iii in W the form of a coiled v wire filament. Within casing H and surrounding the heater filament is disposed a body it of material capable of being ignited by the filament when the latter is raised to a predetermined temperature. The heater 35 element may, if desired, be provided with aprimer of fulminating material, such for example as a mixture of equal proportions of red phosphorus and nitre, to facilitate the ignition of the material of body 2d. Body 2@ may be comprised of any suitable material readily ignitable and capaible upon ignition thereof of producing sumcient heat to melt the securing bodies id of solder or fusible alloy. A suitable material for the purpose is aluminium powder with iron oxide (Therg5 mit) and a retarding agent such as, for instance, quartz sand.

In the modification of Fig. 3, the terminal plate 26, corresponding to the terminal plate ii of Fig. i, has an outwardly projecting hollow gm cylindrical boss 22 within whichis secured, by means of a body iii of fusible solder, one end of the single fusible conductor 83. Surrounding boss 22 is a heater coil 23 which has connection leads 22% extending outwardly through an open- 35 ing 25 in casing to terminals 2?, one of which is shown in the drawing, on the side of easing iii.

"fire connection terminals Q8 of the heating device of Fig. l and the terminals 271 of the heating device of Fig. 3 are adapted to be connected with an auxiliary circuit. Such an auxiliary circuit may be arranged for energization in accordance with an electric condition at a remote point in the main circuit in which fusible conducg5 tors it are connected, or may be arranged for energization from a remote source by manual closing of a switch (not shown). When the heater coil 89 of the embodiment oi Fig. l is raised to a suiheient temperature by flow of 'cur- 5a rent therethrough, the body 2d of ignitable material is ignited, whereupon sufiicient heat is developed to melt the bodies i5. In the embodiment of Fig. 3 the heat developed by heater coil 23 is efiective, without interposition of ignitable g material, to cause melting of the securing body l5. Upon melting oi the solder at the securing points of the fusible conductors, the connection between the fusible conductors and the terminal plate ii of Fig; l, or the terminal plate ii of Fig. 3, is interrupted, in that a portion of the fusible conductors melts and the solder tends to flow away, while the sand or other finely divided refractory filling material, forming an insulat ing incrustation at the openings, inserts itselibetween the fusible conductors and-the terminal plate.

In order to be able to ascertain at some distance whether fuse operation has talren place,

there may be provided an indicating device such as shown in Fig. i. This indicating device comprises a leaf spring iiil one end of which is riv eted or otherwise fixedly secured to casing ill, as shown at 3i, and the other end of which is releasably secured tocasing ill by means of insible solder, as shown at This leaf spring is bowed so that upon melting of the solder 32, due to heating of the casing ll lei/ignition oi the material of body 2d, the end or the leaf spring springs outwardly to the position indicated in broken lines in Fig. 1, thus giving indication that sufficient heat has been produced within casing ii to cause melting of the securing bodies (15 and disconnection of fusible conductors it from terminal plate M.

It is contemplated that, in the practice of the present invention, various modifications in the particular details of construction of the exemplary embodiments illustrated will suggest themselves to those skilled in the art, since, as is believed evident from the foregoing description, the invention is not limited strictly to such details, hence, such modifications as do not depart from the true spirit and scope of the present invention, are intended to be covered by the appended claims.

I claim:

l. A fuse device including in combination, a casing having spaced terminal members, a fusible conductor electrically connected between said members and having one end mechanically joined to one of said members by means of a body of fusible material, a body of sandy arc-quenching material surrounding said conductor adjacent said junction, a body of ignitable material in heat exchange relation to said one terminal member, and an electrically energizable heater element operable ior eliecting ignition of said ignitable.

material.

2. A fuse device including in combination, spaced terminal members, a fusible conductor electrically connected between said members and mechanically joined at one end to one of said members by means of a body of fusible material, a body of ignitable material in heat exchange relation to said body of fusible material, and an electrically energizable heater element operable for efiecting ignition of said ignitable material, thereby to eiiect fusion. and rupture of said junction.

ALFRED M. SCHMIDT. 

